db820c: update default boot device
db820c: update default boot device

The DB820c default GPT was updated such that the 'rootfs' partition is now
expected to be /dev/sda1.

Signed-off-by: Nicolas Dechesne <05fca36dfcf68f7e1c9eaf62b074676ab50a133b@linaro.org>

ndechesne/meta-qcom,ndechesne/meta-qcom,ndechesne/meta-qualcomm,ndechesne/meta-qcom